In systems that are traversed by a medium, in particular a liquid, it often is necessary to detect the throughflow quantity or also the flow velocity of the respective medium.
For this purpose, for example, magneto-inductive throughflow measuring devices (MID) are known. These devices operated according to the principle that charged particles in a medium flowing through a measuring tube are deflected by a magnetic field. Mostly, two coils are arranged on the measuring tube, which in the interior of the measuring tube generate a magnetic field perpendicular to the throughflow direction, wherein parallel to the magnetic field at least two electrodes are placed, on which the charged particles deflected by the magnetic field generate a measuring voltage. This measuring voltage is proportional to the flow velocity of the charge carriers and hence of the medium.
Another measuring method, by which among other things the traversed cross-section of a measuring tube can be determined, uses surface acoustic waves (SAW). For this measuring method the medium is in direct contact with an acoustic waveguide in which surface acoustic waves are excited, wherein the type and frequency of the surface waves are chosen such that a partial coupling out into the medium is effected. The volumetric sound waves generated run through the medium and are reflected on a surface bordering the medium such that they again impinge on the waveguide. There, a part of the volumetric sound waves again is coupled into the waveguide as surface acoustic waves and runs on in the same. On an acoustic receiver that is arranged on the waveguide at a distance from the transmitter, a characteristic signal thus is obtained, which allows conclusions to be drawn regarding the characteristic properties of the medium.
It is the object of the invention to create a compact measuring device that provides for a precise measurement of properties of a medium such as its flow velocity.